Abstract

Mechanoelectrical transduction (MeT) channels embedded in neuronal cell membranes are essential for touch and proprioception. Little is understood about the interplay between native MeT channels and membrane phospholipids, in part because few techniques are available for altering plasma membrane composition in vivo. Here, we leverage genetic dissection, chemical complementation, and optogenetics to establish that arachidonic acid (AA), an omega-6 polyunsaturated fatty acid, enhances touch sensation and mechanoelectrical transduction activity while incorporated into membrane phospholipids in C. elegans touch receptor neurons (TRNs). Because dynamic force spectroscopy reveals that AA modulates the mechanical properties of TRN plasma membranes, we propose that this polyunsaturated fatty acid (PUFA) is needed for MeT channel activity. These findings establish that polyunsaturated phospholipids are crucial determinants of both the biochemistry and mechanics of mechanoreceptor neurons and reinforce the idea that sensory mechanotransduction in animals relies on a cellular machine composed of both proteins and membrane lipids.

(A) Schematic of the circuitry and motor neuron program downstream of TRNs.(B) Withdrawal response elicited by illuminating young adult control and fat-1fat-4 worms expressing ChR2 exclusively in their TRNs with a 470 nm light for one second every 30 seconds at these irradiance values (0.001, 0.002, 0.03, 0.19, and 0.48 mW/mm2), in the presence of all-trans-retinal. A dose-response curve was fitted to the data. At least 10 animals were tested blind to genotype and treatment. Circles and triangles are mean ± sd.(C) Withdrawal response elicited by illuminating young adult worms (control and fat-1fat-4 mutants) expressing ChR2 exclusively in their TRNs with a 470 nm light for one second every 30 seconds at 0.48 mW/mm2 irradiance, in the presence or absence of all-trans-retinal. At least 10 animals were tested blind to genotype and treatment. Bars are mean ± SEM. *Values significantly different from experimental control; Kruskall-Wallis and Dunn's Multiple Comparisons tests, p < 0.001.

(A) AFM force spectroscopy on isolated TRNs expressing GFP. Plot of tether force vs. cantilever retraction speed. Velocities between 1 and 30 µm/s were tested. The equation f3 − f F02 = av was fitted to the data, where f is the tether force at velocity, v, and F0 is the static force, and a is the coefficient characterizing the dynamics of extrusion (; ). Circles are mean ± SEM. The dotted lines indicate the 95% confidence bands for the fit. At least 20 TRNs were tested. Inset shows a graphical representation of the tether extrusion experiment in which an AFM cantilever was coated with peanut lectin and approached onto an isolated TRN and kept in contact for 0.4 s upon retraction, a lipid tube eventually formed in 20% of all contacts.(B) Schematic of the differences in behavior and TRN membrane mechanics in wild-type and fat-1fat-4 worms. Blue: AA-containing phospholipids, gray: phospholipids with less than four unsaturations, and black: cholesterol. Black wedges are measured quantities; the gray wedge shows a predicted difference in membrane thickness.